Efficient ITO-free polymer solar cells with pitch-converted carbon nanosheets as novel solution-processable transparent electrodes

We demonstrate that pitch-converted carbon nanosheet (CNS) films can efficiently function as transparent conducting electrodes for polymer solar cells (PSCs). The solution-processed CNS film was prepared with spin-coating of a cost-effective pitch solution dissolved in dimethylformamide on quartz substrates, followed by stabilization and carbonization treatments to convert the pitch into CNS. The pitch-converted CNS films prepared by the successive heat-treatment process were examined as a novel transparent anode in solar cells, and as a result, PSCs fabricated directly on such CNS electrodes exhibited a high power conversion efficiency of ∼1.7% under 100 mWcm ^-2 illumination and AM 1.5 G conditions. This approach could be highly desirable for advancing the realization of fully printable and flexible low-cost transparent electrodes for indium tin oxide (ITO)-free polymer solar cells.